3-(2-cyano-1-propenyl)-2,2-dimethylcyclopropanecarboxylic acid or its salt can be obtained by hydrolysis of the correspondent ester. As a process for producing such a 3-(2-cyano-1-propenyl)-2,2-dimethylcyclopropanecarboxylate, for example, a reaction of a 4-methoxymethyl-2,3,5,6-tetrafluorobenzyl-3-formyl-2,2-dimethylcyclopropanecarboxylate and 2,2-diethylcyclo(1-cyanoethyl)phosphonate (so-called Horner-Wadsworth-Emmons reaction) is known (for example, JP-A No. 2004-2363).